Bishop James Ussher dissected the Old Testament to analyse the various data and hints there to calculate the time of Creation.

The book of Genesis gives a direct genealogy of Adam’s descendants, through Noah and Abraham, through Moses and on to King Solomon. That’s what all those “begats” are for! More than that, it states the age each man was when his son was born. For example, it says Adam was 130 years old when his son Seth was born (Seth being the ancestor of Noah). From these, it’s easy to calculate timings up to Solomon.

From Solomon onwards, he cross-referenced historical events mentioned in the Old Testament with other historical records to work out timings.

By doing this very painstakingly, Ussher calculated that the world was created 4,000 years before Jesus was born. Ussher was also aware that Dionysus Exiguus, who created the Anno Domini year-counting system which our modern Gregorian calendar incorporates, had calculated the birth of Jesus incorrectly. According to Ussher, Jesus was born 4 years before the date that Dionysus calculated (and labelled “Year One Anno Domini”). Allowing for this 4-year miscalculation, Ussher worked out that the Creation occurred in 4004 BC.

In fact, he went further than that. He decided that the world was created in Autumn, because that’s when the Jewish calendar year starts. He further decided that the world was created at the equinox in Autumn (the first day would logically have equal hours of daylight and nighttime). And, of course, he knew that the world was created on a Sunday – because God rested on the seventh day, which was the sabbath, which was Saturday. So, looking for a Sunday near the Autumnal Equinox in 4004 BC gave him Sunday 23rd October (using the Julian calendar dating, as the Gregorian calendar wasn’t being used in Ussher’s home of Ireland yet). Finally, because the Jewish day starts at sundown, that means the first day started at sundown. The world was therefore created at exactly 6:00pm on Saturday 22nd October, 4004 BC.

Bishop Ussher published his calculations in 1650 AD, under the title ‘Annales Veteris Testamenti, a prima mundi origine deducti, una cum rerum Asiaticarum et Aegyptiacarum chronico, a temporis historici principio usque ad Maccabaicorum initia producto’ (“Annals of the Old Testament, deduced from the first origins of the world, the chronicle of Asiatic and Egyptian matters together produced from the beginning of historical time up to the beginnings of Maccabes”).

However, Ussher wasn’t the only person trying to calculate the age of the Earth – far from it! It was one of the big theological and scientific puzzles in Christendom for centuries. Literally dozens of theologians and philosophers had published (and would continue to publish) their calculations of when the Earth was created as recorded in the Old Testament. Here’s a list from Wikipedia of some other people who published similar calculations. Even renowned scientists like Isaac Newton and Johannes Kepler had a go! So, he was yet another person with yet another calculation of the date of the Earth’s Creation. Yawn.

The only reason we know about Ussher’s calculations and not all these others is because Ussher’s dates were incorporated into some editions of the King James Bible as margin notes throughout the text, and this practice spread to all editions of the King James Bible. This inclusion thus made his calculations “official”, which is why we know them today, and not the others.